Method and system for optically recording and playing back information on a recording medium having magnetization film thereon

Abstract

Disclosed is a method and system for recording and playing back information utilizing a recording medium having a vertical magnetization film on and from which the information is recorded and read out by an optical means, characterized by changing the direction of the magnetic field applied on the recording medium during the application of a recording light beam so as to maintain the recording track of portions of the recording medium on which the previously recorded information is erased by the application of the recording light beam during editing operations.

What is claimed is: 
     
       1. A method for recording, playing back and erasing information utilizing a recording medium having a vertical magnetization film on and from which the information is recorded and having readout by optical means, including a recording beam and a playback beam, means for applying a weak magnetic field on the recording medium, and a tracking servo system operated by a control signal produced by a reflection of the playback beam, the method comprising the steps of: recording the information on the vertical magnetization film to form a recording track, in manner such that a spot of the recording beam is applied, in accordance with the information to be recorded, on the vertical mangetization film whose magnetization orientation is previously unified in a first direction, under the application of the weak magnetic field having a second direction reverse from said first direction;   reproducing the recorded information and erasing desired portions of the recorded information by applying the recording beam on desired portions of the recording track under the application of the weak magnetic field whose magnetic orientation is in said second direction; and   operating the tracking servo at the time the erasing operation is performed so that the recording beam is applied in registry with the original said recording track, thereby erasing the desired portions of said recording track subsequent to the reproduction of the information recorded thereon, and forming new recording tracks accurately on the initial recording track by the operation of tracking servo system.   
     
     
       2. A method as claimed in claim 1, comprising the further step of recording new information on said recording track at the location formed by the erasure, by applying a magnetic field having a magnetic orientation in said first direction. 
     
     
       3. A method as claimed in claim 2, wherein the magnetic orientation is controlled by a polarity switching device responsive to a control signal produced by the tracking servo system, and wherein the erasure step further comprises the step of recording a predetermined sign for indicating a desired change of the magnetization direction at the lead portion of the erased region of the recording track, thereby automatically changing the direction of the magnetic field to said first direction at the time of recording new information. 
     
     
       4. A system for recording and playing back information utilizing a vertical magnetization film on and from which the information is recorded and read out, the system comprising: a source of a recording light beam;   a modulator for modulating said recording light beam in accordance with a signal corresponding to the information to be recorded;   a first optical path for introducing said modulated recording light beam on the surface of the vertical magnetzation film;   a source of a playback light beam;   a second optical path for introducing said playback light beam on the surface of the vertical magnetization film;   a tracking servo mechanism responsive to a control signal produced by a reflection beam of said playback light beam, for controlling the position of a recording track formed on the vertical magnetization film by the application of said recording light beam;   means for applying a weak magnetic field on said vertical magnetization film whose magnetization direction is initially unified in a first direction, during the application of said recording light beam; and   means for changing the direction of said magnetic field to a second and opposite direction during a first recording and subsequent erasure so that the portions of the vertical magnetization film receiving the recording light beam during the erasure of information form a recording track aligned with the first recording track with the operation of said tracing servo mechanism.   
     
     
       5. A system as claimed in claim 4, characterized in that said playback light beam introduced by said second optical path preceds said recording light beam introduced by said first optical path on the surface of said vertical magnetization film during the operation of the system, thereby enabling the operation of said tracking servo mechanism. 
     
     
       6. A system as claimed in claim 4, wherein said means for changing the direction of magnetic field operates to change the direction of the magnetic field during rewriting of information so that the magnetization direction of the portion of the vertical magnetization film on which new information is recorded is reverse from that of the portion on which the erasure was effected.